mirror, mirror. Tests with the freshwater crustacean Daphia (Box) suggesting that the toxicity of a pesticide may change because it persists in the environment.
many widely used pesticides may have unpredictable effects on wildlife as they degrade in the environment, a new study suggests. Chemicals that make up these pesticides are chiral, meaning that they occur as two identical but mirror structures. The researchers who conducted the new study found a "dramatic difference" in toxicity and persistence between chiral, and argues that regulators should therefore consider chirality when the pesticide risk assessment.
Although mirrored versions, or enantiomers of a molecule has the same chemical properties, they can interact with enzymes in different ways. There are about a dozen years, researchers noted that microbes tend to preferentially break down specific enantiomers of persistent pesticides such as DDT and other pollutants. Therefore, the enantiomeric ratio of these pesticides has become asymmetrical in some food chains. The researchers also showed that the enantiomers may vary in their toxicity, although most of this work has been done in the chemicals banned.
Chemist Jay Gan and colleagues at the University of California, Riverside, have decided to examine the pesticides that are widely used today. They examined five common insecticides, including organophosphates such as profenofos, and synthetic pyrethroids, such as permethrin. For all these compounds, one of the enantiomers is at least 10 times more toxic than the other Daphia, a small crustacean often used to assess toxicity.
The researchers also found that the enantiomers differ in two organophosphorus they persist in sediment. For example, one enantiomer of permethrin has become almost twice as common as the other during a year, they report online today in the Proceedings of the National Academy of Sciences. This means that the environmental impact of these pesticides may depend on the behavior of a particular enantiomer, the team concludes. "The difference in terms of risk assessment and regulation could be pretty drastic," Gan said.
Derek Muir National Research Institute on Waters in Burlington, Canada, agrees that the variation of the enantiomers can play a big role in determining ecotoxicity. selective degradation "is important for the risk assessment of pesticides to non-target organisms," he said. The key is that regulators can not get the true picture if they do not take into account changes in the ratio of enantiomers and their individual toxicity, says chemist Charles Wong environment at the University of Alberta in Edmonton, Canada.
Related Sites
the basics isomers, enantiomers, and the like
a recent meeting session on chiral pollutants
information on pesticide regulation
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